1. Field of the Invention
The present invention relates to a non-aqueous electrolyte battery, and more specifically, to a non-aqueous electrolyte battery suitable for use in a high-temperature atmosphere.
2. Description of the Related Art
Recently, there is an increasing demand for a battery that can be used as a power source for equipment used in a high-temperature atmosphere (higher than 100° C.), such as a pressure sensor in a tire. A potential candidate for such a battery includes a non-aqueous electrolyte battery such as a lithium primary battery and a lithium ion secondary battery.
As the non-aqueous electrolyte battery to be used for the above-mentioned purpose, a lithium primary battery using manganese dioxide or graphite fluoride as a positive active material and lithium or a lithium alloy as a negative electrode, and a lithium ion secondary battery using lithium cobaltate or lithium manganate as a positive active material and a carbon material as a negative electrode are considered to be suitable due to their excellent load characteristics and low-temperature characteristics. However, when these batteries are left or used at a high temperature, a carbonic ester (propylene carbonate, ethylene carbonate, methyl ethyl carbonate, etc.) that is a solvent of an electrolyte reacts with the positive active material to generate gas such as carbon dioxide, which causes the batteries to expand.
In particular, when a manganese-containing oxide such as manganese dioxide is used as a positive active material, the above-mentioned generation of gas becomes conspicuous due to the catalyst function of the positive active material. In a temperature region higher than 100° C., such a problem becomes more serious. Furthermore, the following also is found: when a battery discharged by about 50% or more is used in a high-temperature atmosphere or left for a long period of time, gas is generated suddenly due to hydrogen and hydrocarbon such as methane, which causes the battery to expand. In this case, the generation of gas is presumed to be caused by the reaction between a solvent of an electrolyte and lithium at a negative electrode, as well as the reaction between the solvent of the electrolyte and the positive active material.
On the other hand, in the case of an ordinary coin-type primary battery, in order to seal the battery, packing made of polypropylene (PP) (which often is referred to as a “gasket”) mainly is used. Polypropylene is a packing material with sufficient reliability for general use and is inexpensive. However, in a temperature region higher than 100° C. that is close to the melting point of polypropylene, polypropylene is softened to make it impossible to obtain sufficient strength. Therefore, polypropylene is not suitable as a packing material for a battery intended for a high temperature.
As a packing material intended for a high temperature, as described in JP 8(1996)-153500 A, a heat-resistant resin having a melting point of 240° C. or higher (e.g., a tetrafluoroethylene-perfluoroalkoxyethylene copolymer (PFA), polyphenylene sulfide, and polyether ether ketone) was studied.
An olefin-type packing material such as polypropylene, which has been used generally, allows gas generated in a battery to pass therethrough gradually to dissipate out of the battery, whereby an increase in pressure in the battery is alleviated. The packing composed of the above-mentioned heat-resistant resin has sufficient durability even at a high temperature; however, transmittance of gas is very small. Therefore, gas accumulates in the battery, and the battery expands due to an increase in pressure. Needless to say, in the case where glass hermetic seal having hermeticity higher than that of sealing with the heat-resistant packing, the expansion of the battery becomes further conspicuous.
There are various reasons for avoiding expanding a battery. When a battery expands, equipment to be used is damaged, and the contact between electrodes and a current collector becomes insufficient, which decreases battery performance and impairs reliability of the battery.
In order to solve the above-mentioned problem, JP 11(1999)-162511 A (EP 1030399), JP 2000-3724 A (U.S. Pat. No. 6,033,809), JP 2000-123868 A, JP 2000-323171 A, and the like disclose the addition of a cyclic sultone derivative such as 1,3-propanesultone to an electrolyte for the purpose of enhancing cycle characteristics of a non-aqueous electrolyte battery and suppressing the generation of gas. Furthermore, JP 4(1992)-355065 A (U.S. Pat. No. 5,296,319), JP 7(1995)-122297 A, and the like disclose that an acid anhydride is added to an electrolyte to reduce the amount of moisture in the electrolyte so as to enhance storage characteristics of a battery at a high temperature. These additives respectively are relatively effective for suppressing the generation of gas in a battery at a temperature of about 60° C. to 80° C. and enhancing storage characteristics.
In atmospheres having temperatures of 100° C. or higher, these additives are not effective enough for the above purpose.
Furthermore, it also is found that although the above-mentioned additives are sufficiently effective to a battery before discharging or with a small discharge depth, they do not exhibit effects as expected with respect to the battery that has been discharged to some degree.